There is known a heater module used to control the temperature of a battery module made by stacking a number of battery shells, as described in Patent Literature 1.
In Patent Literature 1, a heater body tightly contacts the outer side surface of a casing of a battery pack that stores a number of battery modules, and the heater module is attached to the casing of the battery pack by using a heater unit casing. Also, a heat insulating sheet is placed between the surface of the heater body that faces away from the outer side surface of the casing of the battery pack, and the heater unit casing.